Consumers' appetite for more performance and functionality from a small form factor, portable computing system such as a handheld wireless communications device typically outpaces developments in the power supply technology used in such systems. One of the constraints placed on such power supply circuits is that they be small yet able to deliver a relatively ripple free, regulated dc output voltage at steadily rising current levels (loads). For example, in the context of a smart phone, a switch mode power supply for running the digital logic processing and storage components of the phone needs to provide significantly more current than previous generation cellular phones, yet without being allowed a larger space in which to fit.
One of the bulkier components of a switch mode power supply is the energy storage inductor circuit, which is used to pass the specified load from the input power node to an output node. A filter capacitor is included to smooth out the ripple in the output voltage. As the specified load becomes larger, i.e. greater dc output current, the current rating of the inductor circuit must also increase. This is because, the inductor circuit needs to be able to pass the specified load current without losing efficiency due to increased heat dissipation from higher winding resistance and, in the case of magnetic cores, decreased inductance due to core saturation current. In most cases, an inductor with a higher rated current needs to be physically larger, in order to maintain the same inductance and heat dissipation capability. As performance requirements rise, it becomes more challenging to produce a cost efficient inductor circuit using discrete component inductors that will also fit within the tight confines of modern mobile devices.